Control system



W. l. BENDZ CONTROL SYSTEM March 25, 1952 2 SHEETS-SHEET 1 Filed July 2, 1945 WITNESSES:

ATTOR Y March 25, 1952 w. l. BENDZ CONTROL SYSTEM 2 SHEETS-SHEET 2 Filed July 2, 1945 -|NVENTOR h/a/a emarjfieno z Z BY W7,

ATTORNE Patented Mar. 25, 1952 UNITED STATES Zi ATENT OFFICE CONTROL SYSTEIVI Applicationfiuly ,2, 1945, Serial No. 602,861

3 Claims. 1

My invention relates, generally, to electric drives and control systems for rolling mills and the like and, more particularly, to an electric rive and control system for a reversible mill having reels or other work-handling devices on opposite sides of a roll stand.

In the operation of mills of this general type, the material being rolled or worked, which is usually in the form-f a long thin strip, is passed back and forth through the roll stand while being Wound on one reeland unwound from the other under tension. It is necessary in order to obtain a uniform product to maintain a substantially constant'tension-on the material at all times on bothsides of the roll stand. This is notonly necessary during the normal running of the mill but by means of .a-current'regulator and other necessary apparatus responsive to the load current of the motor and which functions to automatically maintain a predetern'iined constant load current on the motor in accordance with the desired tension to be maintained. Such tension control arrangements require that the regulators be adjusted or recalibrated for different speed ranges of the mill during periods of acceleration and deceleration of the mill, and also toprovide the required stalled tension. These arrangements are also affected by friction and inertia conditionsand, therefore, do not provide for maintaining'a substantially constanttensicn under all operating conditions.

Accordingly, the object'of my invention, generally stated, 'is to provide an improved drive and control system for reversible mills and the like which shall be of simple and economical construction, which may be readily installed and operated, and Whichshall positively function to provide improved operatingresults in controlling tension'through the-entire speed range of the mill from zero to maximum speeds.

A more specific object of my invention is to provide an electric drive of the character described wherein the tension control is proportionalatiall timesto the actual tension on the ill 2 material and is not affected by friction or inertia of the mill.

Another object of my invention is to provide an electric drive of the characterdescribed wherein the operation of the reel motors is controlled directly in accordance with the actual strip .tension.

A further object of my invention is to provide an electric drive of the character described wherein the torque and speed of each reel motor, Whether it is functioning as a generator .or a motor, is controlled entirely by an adjustable voltage booster generator functioning to vary the armature voltage of the reel motor in accordance with actual strip tension.

A still further object of my invention is to pro vide an electric drive of the character described wherein the torque and the speed of each *reel motor is controlled by an adjustable voltage booster generator connectedin series circuit relation with it across the main generator or generator bus and the voltage oi" the booster generator controlled in accordance with strip tension through the use of suitable regulator apparatus controlled or actuated by a strip tensioning 'device.

Another object of my invention is to provide, in an electric drive of the character described, for automatically maintaining a constant tension on the strip of material over a Wide speed range'and Wide rangein percentage reduction of thickness by controlling the reel motors entirely by booster generators so connected as to vary their armature voltages in accordance with strip tension.

Another object of my invention is to provide, in an electric drive of the character described, for reducing the size and inertia of the reel motors and controlling their armature voltages by means of series connected booster generators in order to more effectively maintain the predeterminedconstant tension on the strip of material throughout the entire speed range of the mill and particularly during periods or" acceleration and deceleration.

These and other objects of my invention will become more apparent from the following detailed description when read in conjunction with the drawings, in which:

Figures 1a and lb when placed together as indicated constitute a diagrammatic view of 'an electric drive and control system for a reversible mill embodying the principal features of my invention; and v Fig. 2 is a diagrammatic view of a suitable motor-generator set for the electric drive.

In practicing my invention in the form illustrated, the reel and mill motors are supplied With variable voltage power from a main generator, and provision is made for controlling the excitation of the main generator as well as the excitation of the mill motor to control the speed and direction of operation of the mill. Each reel motor is connected to the main generator in series circuit relation with a booster generator, the excitation of which is controlled by means of an exciter or regulating generator. The excitation of each exciter generator is controlled by a suitable voltage regulator actuated by a strip tensioning device positioned between the roll stand and each reel motor so that the voltage developed by each booster generator is always in accordance with strip tension under stalled and running con-' prising a main roll stand I! I, left and right reels [2 and I3, and left and right tensioning devices [4 and I5 positioned between the roll stand and thereels for rolling a strip of material I6. As shown, the reel I2 is the unwinding reel, and the reel l3 the winding reel with the material moving in the direction of the arrow.

The tensioning devices it and lb per se are not a part of my invention as any suitable type of tensioning device or tensiometer may be used in connection with my electric drive so long as it'functions to apply a suitable transverse force to the strip I6 and thereby subject it to a substantially constant tension throughout the op erating range of the device. Anyone of several known forms of tensioning devices may be used the particular type of device shown being illustrative only.

only one will be described in detail and corresponding parts of the other indicated by the same reference numerals with letter suffixes.

Referring to the tension device I l, it is shown as comprising, in general, a tensioning roll H which is suitably mounted for rotation about the bearing point I 8. This bearing point is on a support l9 which has a center of rotation 2 I. be understood that this provides an eccentric support for the roll 11 so that when the arm 22 of the support i9 is moved back and forth, as indicated by the arrows on opposite sides thereof, the roll I? moves up or down, as the case may be, to vary the tension on the strip it.

The arm 22 is attached to a rotatably mounted crosshead 23 by means of a link 24. One end of the link is attached to an adjustable block 25 carried by the screw 26 which provides for adjusting the position of the block 25 in the crosshead and thereby the effective lever arm of the crosshead acting upon the roll ii. The crosshead 23 is provided with an angular-1y extending arm 21 which carries a suitable weight 23, the angular relation of the arm being such as to cause the force exerted by the roll 5? to be automatically varied over a predetermined range of movement so as to maintain a substantially constant tension on the strip.

It will i It will be understood that by means of this arrangement, the weight 28 causes the roll I! to be urged upwardly against the strip l6 with a force as determined by the weight itself and the position of the adjustable block 25 in the crosshead. It will be further understood, of course, that the reel motor I2 is so controlled as to maintain the position of the strip it and the roll I! as near constant as possible and within the predetermined range or" movement.

The roll stand it is driven by a main motor 3! which is supplied with variable voltage power from a main generator 32. This main generator may be a part of the motor generator set, as shown in Fig. 2, and driven by a suitable motor 33.

A dynamoelectric machine is connected in driving relation with each of the reels. These machines alternately function as motors and generators and will be referred to hereinafter as reel. motors. Thus, reel motor is associated with reel I2, and reel motor 35 with reel i3. These motors in this instance are provided with field windings 34a and 35a which are separately excited from a source of constant voltage excitation, indicated by the positive and negative symbols.

During stalled and normal running operation of the mill, each of the reel motors 34 and 35 is connected across the main generator 32. In other words, the reel motors are connected ,in parallel circuit relation to this generator through suitable switches, which will be referred to hereinafter. It will be understood that by means of this connection, the real motor associated with the unwinding reel is functioning as a generator to regenerate power into the main generator circuit, and the other reel motor on the winding reel is taking power from the main generator.

In order to provide for controlling the operation of the reel motors, a booster generator is connected in series circuit relation with each motor. Thus, the booster generator 36 is connected with motor 34 and the booster generator 8'! with motor 35. These booster generators may constitute a part of the motor-generator set shown in Fig. 2 and are driven at constant speed by the motor 33. The booster generators are provided with series field windings 36a and 31a and separately excited field windings 36b and 31b.

In order to provide for controlling the excitation of the booster generators 36 and 31 in accordance with tension, the excitation of their field windings 35b and 31b is controlled by means of exciter generators or regulating generators 38 and 39. These machines are likewise a part of the motor-generator set shown in Fig. 2, or they may be in a separate motor-generator set along with the source of control voltage, if desired. The regulating generators are each provided with three field windings. In the case of the generator 38, it has a control field winding 38a, a diiferential field winding 38b, and a cumulative field winding 380. The generator 39 likewise has a control field winding 39a, a differential field winding 3%, and a cumulative field winding 390.

It will be noted that in each instance the cumulative field windings 38c and 390 are connected in shunt relation to resistors H and 42 in the reel motor circuits so that these field windings are excited in accordance with the load cur- The difierential field 44 having their primary windings connectedin the reel motor circuits. It will be understood that the difierential field windings 38b and 39b areenergized only in response to sudden changes in the currents flowing in these reel motor circuits.

The energization of the control field windings 38a and 39a is controlled by means of regulators '45 and 4B, which, in turn, are actuated by or in accordance with the movements of the tensioning devices 14 and I5, as shown. Each of the field windings 38a and 39a are connected in a bridge circuit which is controlled by its associated regular. With respect to field winding 38, it will be observed that the bridge circuit comprises resistors 41, 48, 49, and 50 with the field winding 39a connected between the mid-points of these resistors through conductor Resistors 41 and 48 are connected in series and are energized from the control source. The resistors 49 and 50 are likewise connected in series and energized from the control source. These resistors are a part of the regulator 45. This regulator may take any suitable form, but, in this instance, is shown as of the type having two sets of contact fingers 52 and 53 normally insulated from each other and connected to taps 54 on their associated resistors. The regulator 45 is actuated in accordance with the movements of the tensioning device [4 by having its actuating member 55 connected to the crosshead 23 by a link 56. The arrangement is such that when the actuating member 55 of the regulator is moved in opposite directions, the sets of contact fingers 52 or 53 will be successively actuated into engagement to shunt the associated resistor, depending upon the direction in which the actuating member 55 is moved. This, in turn, depends upon the direction of movement of the tension roller H.

In View of the foregoing description of the bridge circuit, it will now be apparent that the regulator 45 functions in response to changes in tension on the strip l5 to so control the voltage developed by the regulating generator 38 as to cause the booster generator 36 to make the necessary adjustment of its voltage to cause the reel motor 34 to so operate as to bring the tension back to its normal desired value. This means, of course, that any slight change in the position of the tension roller 11 causes the reel motor 34 to so function as to restore the roller to its proper position.

The manner in which the booster generator 38 is controlled by its associated regulating generator 38 depends upon whether or not the reel motor 34 is functioning as a motor or a generator. Under the assumed direction of operation of the mill, in this instance, the motor 34 is functioning as a drag generator, and, therefore, the booster generator 36 must develop a voltage which is cumulative with respect to the voltage of the reel motor 34 so that the total voltage output of these two machines exceeds the voltage of the main generator 32. The amount by which this voltage is exceeded determines the torque developed by the reel motor 34 as a drag generator and produces the desired amount of strip tension.

The regulator 41; associated with the tensioning device [5 functions to control the control field winding 35a of the regulating generator 39 in the same manner. In this instance, the bridge circuit comprises resistor 5i and 62 corresponding to resistors 41 and 48 of the other bridge circuit and resistors 63 and 64 corresponding to resistors 49 and 5!) of this other circuit. The field winding 39a is connected between the mid-points of these pairs of resistors through conductor 55. Since the operation of the circuit is the same as the other, it will not be described in further detail.

The pairs of resistors 49-50 and 63-54 of the bridge circuits are normally disconnected from the control source and are connected thereto'and rendered effective by means of a pair of relays 61 and 58.

In this instance, the speed of the mill is controlled by varying the voltage of the main generator 32 and the excitation of the mill motor 3|. The direction of operation of the mill is controlled by controlling the polarity of the generator 32. This is accomplished by means of a pair of reversing relays 59 and 70 provided with operating windings H and 72 which are controlled by a manual controller 66. The excitation of the field winding 32a of the generator is controlled by a rheostat i3, and the excitation of the field winding am of the motor 3| is controlled by rheostat 14. These rheostats are mechanically connected in a well known manner to provide'for first increasing the voltage of the generator to a maximum value and then decreasing the excitation of the motor to a minimum in order to obtain maximum mill speed.

In this instance, the connection of the reel motors to the main. generator 32 is controlled by means of switches '15 and 16.

The mill motor 3| is provided with a dynamic braking circuit including a dynamic braking resistor 7?, and this circuit is controlled by arelay '38 having normally closed contact members 18a and normally open contact members 181).

The connection of the mill motor 3| to the generator 32 is controlled by a switch 79. Each of the reel motor circuits includes a current relay. The relay 8! is in the circuit of the reel motor 34 and the relay 82 in the circuit of the reel motor '35.

The control system includes a control relay 83, the function of which will be described more in detail hereinafter. This relay is controlled by a plurality of push-button switches 84, 85, 86, and 87, which may be termed the tension on, run, stop and tension off switches, respectively. A voltage relay 88 responsive to the main generator voltage cooperates with these switches in effecting the various control operations.

In order to provide for jogging the reel motors in either direction, provision is made for connecting their associated booster generators in series circuit relation with their respective armatures. In the case of the left reel motor 34, its booster generator 35 may be connected in series with is armature by means of switch which is controlled by a pair of jogging relays 89 and 90 which are, in turn, controlled by a pair of pushbutton switches 9i and 92. These switches are selectively operable to energize the jogging relays 3S 59, the operation of either one being effective to energize the switch 85.

shown, the energizing circuit for the winding of switch 56 extends through back contact members 15a of the switch :5 so that this circuit can be completed only when switch 15 is open and the reel motor 34 disconnected from the main genewor The energizing circuit for the opei windings Q4 and S5 of the jogging. relays extends through back contact members 83a'of the control relay 83 so that a jogging operation can be effected only when the control relay is :deenergiaed, which is a condition resulting when the mill motor is disconnected from the main generator.

The right reel motor 35 may be jogged by means of a similar connection. In this instance, the switch 36 is used to connect the reel motor and its booster generator 31 in series circuit relation. The jogging relays are indicated at 91 and 9B. These relays are controlled by the push-button switches 99- and IE0. As in the case of the other circuit, the energizing circuit for the winding IIII of switch 96 extends through back contact members 16a of the switch I6 which connects ,the reel motor 35 to the main generator.

Each of the reel motors is provided with a dynamic-braking circuit. The dynamic-braking circuit for the reel motor 34 includes a resistor I02; for reel motor 35 resistor I03 is included. These dynamic-braking circuits are controlled by relays I04 and I05 which have normally closed contact members IIl la and I05a. These relays are under the control of either their associated jogging relays or the c'ontrol relay 83. As shown, the winding I35 of relay I34 is energized in response to the closure of contact members 89a or 50a of the jogging relays B9 and 90. It is also energized in response to the closure of contact members 83b of the control relay. The same is true with respect to the relay I05 for controlling the dynamic-braking circuit of the reel motor 35. Its operating winding I01 is energized in response to the closure of contact members 31a or 98a of the jogging relays or contact members 830 of the control relay.

In each of the dynamic-braking circuits, provision is made for controlling the efiectiveness of the resistors. With respect to resistor I02, :1- shunting relay I38 normally functions to shortcircuit a portion of the resistor and is controlled by a relay I99 which is responsive to the voltage developed in the dynamic-braking circuit. In the case of the dynamic-braking resistor I03, it is controlled by a shunting relay I III under the control of a voltage relay I I I.

In the operation of the mill, when it is desired to jog the left reel motor 35 to the left, for example, the push-button switch 92 may be actuated to energize the jogging relay 89 through an obvious energizing circuit. The closure of relay 89 energizes the operating winding I06 of relay I34 which opens the dynamic-braking circuit at I its, contact members Ma. The closure of contact members 891) of relay B9 energizes the operating winding 93 of the switch 80 and connects the booster generator 36 in series with the motor 34. The closure of contact members 890 energizes the control field winding 38a of the regulating generator 38 through resistor II and resistor II2. It will be obvious at this point that if the other jogging relay 93 is operated in response to closure of the push-button switch 9|, the field winding 38a will be energized in the oppos'ite direction through resistor 58 and resistor II3.

Upon the establishment of these connections, the regulating generator 38 causes the booster generator 36 to develop sufiicient voltage to 0perate the reel motor 33 to effect the desired jogging operation.

The right reel motor 35 may be jogged in the same manner by operating either one of the push-button switches 99 and I00, in which event the field winding 39a of regulating generator 39 will be energized through one or the other of resistors H4 and H5.

' fAssuming that the mill has been threaded and is now in condition for a rolling operation to commence; and it is desired to initially establish the desired tension on both sides of the roll stand, this may be accomplished by actuating the manual controller 66 from its off position to either its right or left positions, as indicated, to efiect the operation of either one of the reversing switches I59 or 10.. The closure of the reversing switch which is operated causes the field winding 32a of the main generator 32 to be connected to develop voltage of the desired polarity, and it may be adjusted or raised to the desired value by the generator rheostat I3. Under this condition the voltage relay 88 is energized, and its contact members 88:; are closed and 2281) opened. The closure of contact members 88a of this relay provides a holding circuit for the operated reversing switch 69 or ID and prevents a reversal of the generator voltage by actuating the manual controller 66 to the opposite direction until the voltage of the main generator 32 is reduced to a suffioiently low value to make such a reversal harmless to the equipment.

In order, however, to establish the initial tension, the tension on push-button switch 84 is first closed before the voltage of generator 32 is raised, which energizes the control relay 83 through a circuit extending from positive through contact members 8812, switch 84, conductor I2I, switch 81, conductor I22, contact members 96b, conductor I23, contact members 882), conductor I23, and the operating winding I25 of the control relay to negative. At the same time, the operating windings I26 and IE7 of relays 6'! and 68 are energized through parallel circuits and these relays close the energizing circuits to the resistors associated with the regulators 45 and 46.

The closure of both of the relays 5'! and 38 to energize the regulators and the closure of the control relay 83 establishes an energizing circuit for relays I5 and I6 to connect the reel motors to the main generator. These circuits extend from positive, through contact members 83d and 68a, conductor I20, contact members 6 1a, conductor I29, contact members 800 and operating winding I30 to negative. This circuit operates the relay I5. The energizing circuit for relay I6 extends from point I3I in the previously described circuit through conductor I32, contact members 960 and the operating winding I33 of relay I6 to negative.

As soon as sufficient current flows in the reel motor circuits, the current relays 3! and 82 are operated to close their contact members 8Ia and 82a in the control circuit.

It will now be apparent that with the main generator 32 energized and the reel motors connected thereto and the regulators 45 and 46 rendered efiective, the regulator generators 38 and 39 will be so controlled as to cause the booster generators 36 and 31 to control their respective reel motors 34 and 35 in such manner as to establish stalled tension of such value as determined by the adjustment of the tensioning devices Id and I5.

In the case of the reel motor I2 which is functioning as a drag generator, the voltage developed by its associated booster generator 33 will be in such direction with respect to the voltage of the main generator as to cause the reel motor to develop the necessary torque in amount and direction to establish the desired amount of back tension.

In the case of the reel motor I3, which isfunctioning as a motor, its booster generator voltage will be such as to cause its torque to be in the desired direction and of the desired value to producev the necessary pulling tension.

If it is now desired to initiate the operation of the mill, the run push-button switch 85 may be closed which establishes an energizing circuit for the switch 18 to open the dynamic braking circuit for the mill motor 31, and for the switch 19 to connect the mill motor 3| to the main generator. These circuits extend from the positive through contact members 83c of the control switch, conductor IZI, switch 85, switch 86 which is normally closed and conductor I35 where they divide, one branch going directly to the winding 128 which closes switch 78, and the other branch going through contact members 82a and 8la, conductor I36,

, contact members 18bwhich are row closed, and

the operating winding [31 of switch 19.

Contact members 19a of this switch function to complete the motor circuit, while the contact members 78a of switch 18 open the dynamic braking circuit of the mill motor (it. sure of contact member 181) establishes a holding circuit around the run push-button switch 85 so that it may be released to its normal open position. This operation places the mill in running condition, and its speed is controlled by the generator and motor field rheostats 13 and M as described hereinbefore.

In the event that it is desired to stop the mill, the stop push-button switch 86 may be actuated, which deenergizes the switch 19 and disconnects the mill motor from the main generator. It is to be understood, however, that in stopping the mill, the speed thereof may be reduced by operating the field rheostats E3 and 14 in the reverse direction from that in which they were operated when increasing the speed of the mill to normal running value.

It will be noted that as soon as the switches 15 and 16 were closed to connect the reel motors to the generator, the jogging control circuits were rendered ineiiective because of opening of back contact members 15a and 16a of these switches. This prevents any attempt being made to effect a jogging operation while the mill is running to efiect a rolling operation. The operation of the control relay 83 also opens at its contact members 83a, the energizing circuit for the jogging relays 39, 95) 9'1, and 98.-

While the field rheostats l3 and '54 have been shown as manually operated devices, it will be understood that these rheostats may be motoroperated and controlled from a remote point in a well known manner. The same is true with respect to the adjustment of the tensioning devices l4 and 15 which are shown for manual adjustment. The hand wheels led and lb may be replaced by a suitable remote control arrangement.

In view of the foregoing, it will be apparent that I have provided an electric drive and control system for a reversible mill wherein the tension on the material is controlled in such manner as to be unaffected by friction and inertia. The torque and speed of operation of the reel motors are controlled entirely in accordance with the tension on the material by means of adjustable booster generators so connected as to properly control the armature voltages of the reel motors. The tensioning. devices so'function as to provide thenecessary amount of tension on both sides of the roll stand, and

The 010- their movements are utilized to control the voltage regulators which through the regulating generators and booster generators cause the torques and speeds of the reel motors to be so maintained as to balance the force exerted upon the strip by the tensioning devices.

In view of the fact that the torque and speed of the reel motors are controlled solely in response to tension, a predetermined constant tension may be maintained on the strip under all operating conditions and regardless of the speed of the mill or the degree of reduction in the material being rolled. Stalled tension is also readily obtained for the reason that the regulating system functions to effectively control the speed and torque of the reel motors equally as well when stalled as when running.

Furthermore, in view of the nature of the regulating control used for the reel motors, the mill may operate over a wide range without recalibration or adjustment of control equipment.

In view of the fact tha the reel motors are controlled solely by series connected booster generators and not by shunt field control, the size of the reel motors may be held to a minimum so that their inertia is likewise reduced to a minimum which contributes to the degree of accuracy to which the tension may be held. This is particularly true during periods of acceleration and deceleration. The use of seriescomiected boosters effects a more rapid response of its reel motors and provides a much Wider range of control thereof than that obtainable by shunt field control.

While I have shown and described a specific embodiment of my invention, it will be apparent to those skilled in the art that changes and modifications may be made therein without departing from the principles thereof.

I claim as my invention:

1. An electric drive comprising, a main motor, a pair of motors each having a mechanical connection with the main motor, a main generator for supplying variable voltage power to said motors, a booster generator individual to each motor, a regulator exciter individual to each booster generator operable to control the excitation thereof, a regulator for controlling the excitation of each regulator exciter, said regulators being actuated in accordance with operating conditions of their mechanical connections with the main motor, means operable to connect the booster generators in closed circuit relation with their associated motors and control the operation of their associated regulator exciters to selectively operate each motor in either direction of rotation to efiect jogging operations, means operable to connect said booster generators in series circuit relation with their associated motors to the main generator and render the regulators effective to control their associated regulator exciters, thereby to establish stalled tension operating conditions of the mechanical connections on opposite sides of the main motor, and means operable thereafter to connect the main motor to the main generator.

2. The combination with a motor of a dynamoelectric machine mechanically connected to the motor, a booster generator, control means operable to connect the dynamoelectric machine and booster generator to a source of power in series circuit relation, a regulator generator for controlling the excitation of the booster generator, said regulator generator having a plurality of field excitation windings, means for exciting one of said field windings in accordance with abrupt changes in the load current of the dynamoelectric machine, means for exciting another of said field windings in accordance with the amount of load current of the dynamoelectric machine, a regulator operable to control the excitation of another of said field windings, said regulator being responsive to an operating condition of the mechanical connection, thereby to cause said booster generator to so control the efiective voltage of the dynamoelectric machine as to maintain the necessary speed relation between the motor and the dynamoelectric machine to maintain a predetermined operating condition of the mechanical connection.

3. A control system comprising, a motor, an additional motor connected in operating relation with said motor, a booster generator connected in series circuit relation with the additional motor to a power source, means including a regulator for controlling the exgitation of the booster generator, and a movable device responsive to an operating condition dependent on operating relations between said motors, said regulator being controlled in accordance with the movement of the device, thereby to so control the operation of the additional motor as to maintain the device within its operating range.

4. A control system comprising, a motor, a booster generator connected in series circuit relation with the motor to a power source for controlling the speed of the motor, a regulator exciter for controlling the excitation of the booster generator, a movable device responsive to an operating condition controlled by the motor, and regulator means controlled by the device for controlling the excitation of the regulator exciter, thereby to so control the speed of the motor as to maintain the device within its operating range.

5. A control system comprising, a main motor, an auxiliary motor having a mechanical connection with the main motor, a variable voltage generator for supplying power to the main and auxiliary motors, a booster generator connected in series with the auxiliary motor, means operable to control the polarity and value of the voltage of the power source for controlling the speed and direction of operation of the main motor, and regulator means responsive to an operating condition of the mechanical connection between the main and auxiliary motors for controlling the voltage of the booster generator, whereby the auxiliary motor functions as a motor when the motors operate in one direction and as a drag generator when the motors operate in the other direction and develops the necessary torque to maintain the operating condition of said mechanical connection within a, predetermined operating range throughout the speed range of the main motor.

6. A control system comprising, a main motor, a pair of auxiliary motors each disposed to maintain a predetermined operating condition with the main motor, a main generator for supplying power to said main and auxiliary motors, said motors bein connected in parallel circuit re lation with the main generator, a source of constant voltage excitation for the auxiliary motors, an auxiliary generator connected in series circuit relation with each auxiliary motor, said auxiliary generators functioning to vary the effective voltage applied to the auxiliary motors from the main generator, an exciter connected to the field winding of each auxiliary generator, a regulator operable to control the excitation of each exciter, a movable tensioning device interposed between the main motor and each auxiliary motor, said tensioning devices being inherently operable within a predetermined operating range to maintain a substantially constant tension condition, and means connecting each regulator to its associated tensioning device for efiecting the operation of the regulators in accordance with the movements of the tensioning devices to thereby so control the operation of the auxiliary motors as to maintain the tensioning devices within predetermined operating ranges.

7. In a control system for a main motor and a pair of dynamoelectric machines each having a mechanical connection with the main motor, a main generator for supplying power to the main motor and the dynamoelectric machines, an auxiliary generator individual to each dynamo electric machine, a movable tensiometer operable in response to an operating condition of each of said mechanical connections, regulator means responsive to the movements of the tensiometer for controlling the excitation and thereby the voltage of the auxiliary generators, said regulator means being normally ineffective, first control means individual to each dynamoelectric machine for connecting their associated auxiliary generators in series circuit relation therewith to eifect the operation of the dynamoelectric machines in either direction to effect joggin operations of the dynamoelectric machines independently of the main generator, said auxiliary generators supplying the necessary power to so operate the dynamoelectric machines, and second control means operable to efiect the connection of the dynamoelectric machines to the main generator in parallel circuit relation and in series circuit relation with their respective auxiliary generators and to render the regulating means effective to control their associated auxiliary generators to establish a stalled tension condition of the mechanical connection.

8. In a control system a main motor, a pair of dynamoelectric machines mechanically connected in operating relation with the main motor, a main generator for supplying power to the main motor and the dynamoelectric machines, an auxiliary generator individual to each dynamoelectric machine, a movable tensiometer opcrable'in response to an operating condition of the mechanical connection between the main motor and each of the dynamoelectric machines, regulator means responsive to the movements of the tensiometer for controlling the excitation and thereby the voltage of the auxiliary generators, said regulator means being normally inefiective, firstcontrol means individual to each dynamoelectric machine for connecting their associated auxiliary generators in series circuit relation therewith to efiect the operation of the dynamoelectric machines in either direction to efiect jogging operations independently of the main generator, said auxiliary generators supplying the necessary power to so operate the dynamoelectric machines, second control means operable to' eifect the connection of the dynamoelectric machines to the main generator in parallel circuit relation and in series circuit relation with their respective auxiliary generators and to render the regulating means effective to control their associated auxiliary generators to establish stalled tension condition of the mechanical connections, third control means rendered effective by the operation of the second control means operable to connect the main motor to the UNITED STATES PATENTS main generator to establish running connections, Number Name Date and fourth control means operable to control th 1 865 410 Byles June 23 1932 polarity and value of the voltage of the main 2:214:355 Tiselius et a1 Sept 1940 generator to effect the running of the main mot r a 2 214 617 Kenyon Sept 1940 and dynamoelectric machines in either direction. 2:325:381 Edwards et a1 July 27 1943 WALDEMAR BENDZ- 2,363,684 Montgomery Nov. 23, 1944 2,401,147 Field et a1 May 28, 1946 REFERENCES CITED 2,437,973 Schmitz Mar. 16, 1948 The following references are of record in the 1 2,444,248 Crever June 29, 1948 file of this patent: 

